Storage servers provide intrinsic error checking. Dataset servers can
trust them without alleviating data integrity : if an undetected error
occurs while retrieving data, it will be detected by DAP server at the
next stage.

The critical part along the path from data store to DAP Server is
dataset server to DAP server transmission: dataserver may be on an
untrusted host, and return faked, though valid, data.

A byzantine server detection system should validate data received from
untrusted hosts and be able to score them with some “trust-level”.

Dataset requests are deterministic: whatever server we request,
response should be the same, bit-per-bit.

When DAP server requests for a dataset, it may [*] ask to another
dataset server to perform the same request and to return just a
checksum of the response [†].

DAP server checksums dataset received from first server and compares
this to the value returned by the second one.

If values don’t match, both servers are tagged with a byzantine
warning flag, and the same request is re-issued to some other
hosts. When we have a validated response, we can unflag original hosts
which gave valid response.